Modified Zeolites as Alternative Adsorbents for PFAS Removal: A Comparative Study with Granular Activated Carbon

Per- and polyfluoroalkyl substances (PFAS) are persistent and mobile contaminants of global concern, and while granular activated carbon (GAC) is widely used for their removal, it is limited by high regeneration and disposal costs. This study investigates surface-modified clinoptilolite zeolites as low-cost and thermally regenerable alternatives to GAC for PFAS removal from water. Natural clinoptilolite was modified through acid washing, ion exchange with Fe³⁺ or La³⁺, grafting with aminosilane (APTES) or hydrophobic silane (DTMS), dual APTES–DTMS grafting, and graphene oxide coating. Adsorption performance was evaluated for perfluorooctanoic acid (PFOA, C8) and perfluorobutanoic acid (PFBA, C4) at 100 µg L⁻¹ in single and mixed-solute systems, with an additional high-concentration PFOA test (1 mg L⁻¹). Raw zeolite showed limited PFOA removal (4%), whereas dual-functionalised APTES+DTMS zeolites achieved up to 93% removal, comparable to GAC (97%) and superior to single-silane or metal-exchanged variants. At lower concentrations, modified zeolites effectively removed PFOA but showed limited PFBA removal (< 25%), highlighting ongoing challenges for short-chain PFAS. Overall, the results demonstrate that dual-functionalised clinoptilolite zeolites represent a promising and scalable platform for PFAS remediation, particularly for mid- to long-chain compounds, provided that strategies for enhancing short-chain PFAS binding are further developed.